Bioaccumulation of potentially toxic elements by submerged plants and biofilms: A critical review

Silicate-based mineral materials promote submerged plant growth: Insights from plant physiology and microbiomes

Restoring submerged plants naturally has been a significant challenge in water ecology restoration programs. Some silicate-based mineral materials have shown promise in improving the substrate properties for plant growth. While it is well-established that silicate mineral materials enhance submerged plant growth by improving salt release and reducing salt stress, the influence of rhizosphere microorganisms on phytohormone synthesis and key enzyme activities has been underestimated. This study focused on two typical silicate mineral materials, bentonite and maifanite, to investigate their effects on Myriophyllum oguraense from both plant physiology and microbiome perspectives. The results demonstrated that both bentonite and maifanite regulated the synthesis of phytohormones such as gibberellin (GA) and methyl salicylate (MESA), leading to inhibition of cellular senescence and promotion of cell division. Moreover, these silicate mineral materials enhanced the activity of antioxidant enzymes, thereby reducing intracellular reactive oxygen species levels. They also optimized the structure of rhizosphere microbial communities, increasing the proportion of functional microorganisms like Nitrospirota and Sva0485, which indirectly influenced plant metabolism. Analysis of sediment physicochemical properties revealed increased rare earth elements, macronutrients, and oxygen content in pore water in the presence of silicate materials, creating favorable conditions for root growth. Overall, these findings shed light on the multifaceted mechanisms by which natural silicate mineral materials promote the growth of aquatic plants, offering a promising solution for restoring aquatic vegetation in eutrophic lake sediments.

Fate of heavy metals in ecosystems of dam reservoirs: Transport, distribution and significance of the origin of organic matter

In this article, a multivariate analysis of the parameters determining the transport and fate of selected heavy metals in the water - bottom sediment interface was carried out. The studies were carried out in the summer season of 2019 at Nielisz Reservoir (southeastern Poland, Lublin Voivodeship). Finally, a previously unknown factor related to the quality of organic matter was identified. Autochthonous organic matter was shown to promote the accumulation of the studied heavy metals. To date, the significance of the origin of organic matter in the context of the transport and fate of heavy metals in retention reservoirs has rarely been reported in the scientific literature. More than that, this factor was not considered an important component in the process of heavy metal deposition in bottom sediments. However, it turns out that not only the quantity of organic matter, but also its quality plays an important role in the circulation of heavy metals in retention reservoir ecosystems. It was found that autochthonous organic matter promotes the accumulation of the studied heavy metals. It can be assumed that, in a sense, it plays the role of a catenary ("hub") controlling the fate of heavy metals in the water-sediment system. It has also been conjectured that, in a sense, OMS may reflect the potential for heavy metal assimilation by aquatic vascular plants (mainly of the C3 group). Plants with a photosynthetic pathway similar to the C3 group generally have a much lower enrichment in the 13C isotope (δ13C from -38‰ to -22‰). In our case, the lowest δ13C-TOCS value was -24.05‰, and the average for the whole reservoir was -21.53‰. In addition, it was observed that quantitative changes in the isotopic composition of total organic carbon δ13C-TOCS, corresponded with changes in the content of the heavy metals studied in entrapped sediments.

Effects of long-chained perfluoroalkyl acids (PFAAs) on the uptake and bioaccumulation of short-chained PFAAs in two free-floating macrophytes: Eichhornia crassipes and Ceratophyllum demersum

Short-chained perfluoroalkyl acids (PFAAs, CnF2n+1-R, n ≤ 6) have merged as global concerns due to their extensive application and considerable toxicity. However, long-chained PFAAs (n ≥ 7) featured with high persistence are still ubiquitously observed in aquatic environment. To understand the uptake behavior of short-chained PFAAs in aquatic macrophytes, the uptake kinetics, bioconcentration, and translocation of short-chained PFAAs (3 ≤n ≤ 6) in two typical free-floating macrophytes (Eichhornia crassipes and Ceratophyllum demersum) were investigated in the treatments with and without long-chained PFAAs (7 ≤n ≤ 11). Results showed that short-chained PFAAs can be readily accumulated in both E. crassipes and C. demersum, and the uptake of short-chained PFAAs fit the two-compartment kinetic model well (p < 0.05). In the treatments with long-chained PFAAs, significant concentration decreases of all concerned short-chained PFAAs in E. crassipes and PFAAs with n ≤ 5 in C. demersum were observed. Long-chained PFAAs could hinder the uptake rates, bioconcentration factors, and translocation factors of most short-chained PFAAs in free-floating macrophytes (p < 0.01). Significant correlations between bioconcentration factors and perfluoroalkyl chain length were only observed when long-chained PFAAs were considered (p < 0.01). Our results underlined that the effects of long-chained PFAAs should be taken into consideration in understanding the uptake and bioaccumulation behaviors of short-chained PFAAs.

Development and implementation of a novel mechanized planting method for ecological restoration of aquatic environments using degradable nutrition pots

Submerged plants play a significant role in the remediation and purification of polluted water bodies. Reconstruction of submerged plants has been considered as an important ecological method to restore aquatic ecosystems. However, large-scale and efficient plantation of submerged plants in water restoration is a huge challenge. This paper proposes a novel mechanized planting method for submerged plants utilizing nutrition pots as planting units. Firstly, the details of the mechanized planting method were introduced. The mechanized planting method involves pre-planting the reproductive bodies of submerged plants in degradable nutrition pots, and then implanting them into the underwater soil through a planting device. Secondly, the interaction force between the nutrition pot and the soil was measured. It was found that the implantation force of nutrition pots increases with planting velocity. The planting force shows a significant increase trend when the water content in the soil decreases. Thirdly, the deformation of the nutrition pot was studied through simulations. It was discovered that the deformation of the nutrition pot mainly occurs at the bottom and the side walls near the bottom, and the limited deformation ensures the integrity of the nutrition pot. Finally, a planting device with a linear motion mechanism was designed, and a typical submerged plant, Vallisneria natans was tested, using agricultural paper seedling containers as the nutrition pots. It was demonstrated that the mechanized device successfully planted submerged plant nutrition pots into the soil, and the submerged plants survived and showed a clear growth trend. The mechanized planting method of submerged plants proposed in this article is expected to provide a new and friendly technology for ecological restoration of water source.

Evaluation of succulent plants Echeveria elegans as a biomonitor of heavy metals and radionuclides

This work evaluates the use of Echeveria elegans as a biomonitor of metals and radionuclides, using semi-urban soils as a study area. The study area is exposed to various trace elements of concern for various social groups in nearby localities. The quantification of metals and radionuclides was performed by X-ray fluorescence spectrometry and gamma spectrometry, respectively. Cumulative frequency distribution curves, descriptive statistics, and multivariate analysis were used to estimate the local geochemical baseline and identify geochemical and anthropogenic patterns of metals and radionuclides from topsoil and E. elegans. The evaluation of contaminants and the contribution of possible exposure routes (topsoil and atmospheric deposition) was performed with the enrichment factor (EF) and the relative concentration factor (CFR). The results suggest that the plant does not present significant physical stress due to the environmental conditions to which it was exposed. Likewise, it can bioaccumulate heavy metals from natural and anthropogenic sources. The quantification of radionuclides in the plant is below the detection limits, indicating a low bioavailability and transfer factor. The CFR and EF results showed that the plant accumulates metals from the topsoil and atmospheric deposition. The bioaccumulation mechanism would be related to the functioning of Crassulaceae Acid Metabolism (CAM). In topsoil, the organic acids of the plant would modify the solubility of the metals present in an insoluble form in the soil, acting as ligands and, subsequently, following the transport route of these metabolites. In atmospheric deposition, the metals deposited in the leaves would be incorporated into the plant through the opening of the stomata because of the capture of CO2 (at night, day, or during environmental stress) by the CAM. Overall, the evidence showed that the succulent can be used as a biomonitor of heavy metals. However, additional studies are required to determine its usefulness as a radionuclide biomonitor.

Heavy metal spatial distribution, source analysis, and ecological risks in the central hilly area of Hainan Island, China: results from a high-density soil survey

The presence of heavy metals in soil has gained considerable attention due to their potential risks to ecosystems and human health. In this study, a thorough soil investigation was performed in the hilly region of central Hainan, which was formerly regarded as an area with the highest ecological environmental quality. A total of 7094 soil samples were systematically collected with high density over a large area. Simultaneously, a detailed investigation was conducted on the surrounding environment of each sampling point, including environmental factors such as soil, land use and crop types. The soil samples were analysed for heavy metals, pH, organic matter, and other parameters. The soil heavy metal pollution level, ecological risk and health risk were evaluated using the geo-accumulation index and the potential ecological risk index. The findings showed that the average contents of the heavy metals As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in the soil were 1.68, 0.042, 24.2, 6.49, 0.0319, 7.06, 29.6 and 49.8 mg·kg-1 respectively. Except for Hg, the mean values of the other heavy metals were either lower than or similar to the background values of Hainan. Also, only a few localised areas showed contamination by heavy metals. The primary sources of heavy metals, identified by a positive matrix factorisation model, could be categorised into four types: natural sources related to the soil formation process from acidic intrusive rocks (such as granite); natural sources primarily influenced by atmospheric deposition; anthropogenic sources associated with agricultural activities; and natural sources related to the soil formation process from middle-mafic intrusive rocks and black shales. The correlation analysis and variance analysis findings suggested that the content of heavy metals in the soil was primarily associated with the parent rock. The study area generally had low heavy metal levels and was not significantly polluted. However, agricultural activities still affected the enrichment of heavy metals. Therefore, it is imperative to remain vigilant about the ecological risks linked to soil heavy metals while continuing land development and expanding agricultural activities in the future. These findings indicate that conducting high-density soil surveys can enhance our understanding of regional soil heavy metals and enable reliable recommendations for agricultural planning. Whether in areas with low pollution risk or potential pollution risk, it is recommended that high-density soil surveys be conducted provide scientific guidance for further agricultural development.

Low toxicity of magnetite-based modified bionanocomposites with potential application for wastewater treatment: Evaluation in a zebrafish animal model

In recent years, the escalating concerns surrounding environmental pollution and the need for sustainable wastewater treatment solutions have underscored the significance of developing technologies that can efficiently treat wastewater while also reducing negative ecological effects. In this context, our study aims to contribute to the advancement of sustainable technologies for wastewater treatment, by investigating the effects that bare magnetite nanoparticles and those functionalized with the enzyme laccase could have in an aquatic animal, zebrafish, at various life cycle stages. Exposure to magnetite nanoparticles shows some effects on embryo hatching, survival rates, or larval behavior at higher concentrations. For both treatments, the hatching percentages were close to 80% compared to 93% for the control group. At the end of the observations in larvae, survival in all the evaluated groups was higher than 90%. Additionally, we evaluated the accumulation of nanoparticles in various stages of zebrafish. We found that, although there was accumulation during embryonic stages, it did not affect normal development or subsequent hatching. Iron levels in different organs such as gills, muscles, gastrointestinal tract, and brain were also evaluated in adults. Animals treated with a mix of food and nanoparticles at 10 μg/mL (Food group) presented a higher concentration of iron accumulation in muscle, gastrointestinal tract, and gills compared to the untreated control group. Although iron levels increased depending on the dose and exposure method applied, they were not statistically significant from the control groups. Our findings suggest that bionanocomposites evaluated here can be considered safe for removal of contaminants in wastewater without toxic effects or detrimental accumulation fish's health.

The Role of Sediment Ingestion in Exposing Bottom-Feeding Fish to Chemical Elements

Digesta were collected from the intestines of seven species of bottom-feeding fish to better understand the role of incidental ingestion of sediment in exposing fish to inorganic contaminants. A composite sediment tracer variable, based on concentrations of Co, Cr, Ni, Ti, V, and Y in digesta and in sediment, was calculated to estimate sediment content of digesta. Concentration factors (mg/kg in digesta divided by mg/kg in sediment) of eight elements of interest were linearly regressed on this tracer variable. The relative importance of sediment ingestion to oral exposure was quantified. Zinc, Cd, and Cu were ingested mainly from sediment-free food. Arsenic, Cr, Ni, Al, and Pb, in contrast, were ingested mainly from sediment. As an example, 93% of the Ni in digesta from a brown bullhead (Ameiurus nebulosus) was from sediment and only 7% from food. Regressions of Al and Pb in digesta of suckers (Catostomidae) suggested an additional oral source, possibly from oxides coating biotic or abiotic surfaces. Overall, concentrations of 12 of 21 elements studied were positively correlated with sediment content (p < 0.005). Including sediment ingestion as a pathway for bottom-feeding fish is essential for accurately estimating exposures in toxicological studies. Environ Toxicol Chem 2024;00:1-11. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Parabens as environmental contaminants of aquatic systems affecting water quality and microbial dynamics

Among different pollutants of emerging concern, parabens have gained rising interest due to their widespread detection in water sources worldwide. This occurs because parabens are used in personal care products, pharmaceuticals, and food, in which residues are generated and released into aquatic environments. The regulation of the use of parabens varies across different geographic regions, resulting in diverse concentrations observed globally. Concentrations of parabens exceeding 100 μg/L have been found in wastewater treatment plants and surface waters while drinking water (DW) sources typically exhibit concentrations below 6 μg/L. Despite their low levels, the presence of parabens in DW is a potential exposure route for humans, raising concerns for both human health and environmental microbiota. Although a few studies have reported alterations in the functions and characteristics of microbial communities following exposure to emerging contaminants, the impact of the exposure to parabens by microbial communities, particularly biofilm colonizers, remains largely understudied. This review gathers the most recent information on the occurrence of parabens in water sources, as well as their effects on human health and aquatic organisms. The interactions of parabens with microbial communities are reviewed for the first time, filling the knowledge gaps on the effects of paraben exposure on microbial ecosystems and their impact on disinfection tolerance and antimicrobial resistance, with potential implications for public health.

Gene co-expression networks unravel the molecular responses of freshwater hydrophytes to combined stress of salinity and cadmium

Salinization in freshwater lakes is becoming a serious global environmental problem, especially in lakes of plateaus such as south-western plateau of China. However, limited information is available about the molecular response of freshwater hydrophytes to salinity under multiple stress. In the present study, a weighted gene co-expression network (WGCNA) was used to identify the modules of co-expressed genes in the physiological and biochemical indicators of Pistia stratiotes to determine its molecular response to salinity (NaCl) alone and when combined with cadmium (Cd). The physiological and biochemical indicators showed that P. stratiotes improved its salt tolerance by enhancing photosynthetic abilities, reducing oxidative stress, and inducing osmoprotectant generation. Morever, addition of NaCl reduced the Cd accumulation in P. stratiotes. Transcriptome and WGCNA analysis revealed that the pathways of alpha-linolenic acid metabolism, ribosomal, flavonoid biosynthesis, and phenylpropanoid biosynthesis were significantly enriched in both treatments. Genes associated with photosynthesis-antenna proteins, nitrogen metabolism, and the acid cycle pathways were only expressed under salinity stress alone, while the proteasome pathway was only significantly enriched in the combined salinity and Cd treatment. Our findings provide novel insights into the effects of salinization on aquatic plants in freshwater ecosystems and the management of aquatic ecosystems under global change.

Environmental behaviors of emerging contaminants in freshwater ecosystem dominated by submerged plants: A review

Persistent exposure of emerging contaminants (ECs) in freshwater ecosystem has initiated intense global concerns. Freshwater ecosystem dominated by submerged plants (SP-FES) has been widely constructed to control eutrophic water. However, the environmental behaviors (e.g. migration, transformation, and degradation) of ECs in SP-FES have rarely been concerned and summarized. This review briefly introduced the sources of ECs, the pathways of ECs entering into SP-FES, and the constituent elements of SP-FES. And then the environmental behaviors of dissolved ECs and refractory solid ECs in SP-FES were comprehensively summarized, and the feasibility of removing ECs from SP-FES was critically evaluated. Finally, the challenges and perspectives on the future development for ECs removal from SP-FES were prospected, giving possible research gaps and key directions. This review will provide theoretical and technical support for the effective removal of ECs in freshwater ecosystem, especially in SP-FES.

Phytoremediation of toxic chemicals in aquatic environment with special emphasis on duckweed mediated approaches

The discharge of toxic chemicals into water bodies and their linked detrimental effects on health is a global concern. Phytoremediation, an environment-friendly plant-based technology, has gained intensive interest over the last decades. For the aquatic phytoremediation process, the commonly available duckweeds have recently attracted significant attention due to their capacity to grow in diverse ecological niches, fast growth characteristics, suitable morphology for easy handling of biomass, and capacity to remove and detoxify various potential toxic elements and compounds. This review presents the progress of duckweed-assisted aquatic phytoremediation of toxic chemicals. A brief background of general phytoremediation processes, including the different phytoremediation methods and advances in understanding their underlying mechanisms, has been described. A summary of different approaches commonly practiced to assess the growth of the plants and their metal removal capacity in the phytoremediation process has also been included. A vast majority of studies have established that duckweed is an efficient plant catalyst to accumulate toxic heavy metals and organic contaminants, such as pesticides, fluorides, toxins, and aromatic compounds, reducing their toxicity from water bodies. The potential of this plant-based phytoremediation process for its downstream applications in generating value-added products for the rural economy and industrial interest has been identified.

Single and combined toxicity of polystyrene nanoplastics and arsenic on submerged plant Myriophyllum verticillatum L

The contamination of nanoplastics (NPs) and heavy metals (HM) in water bodies has caused widespread concern, while their effects on submerged plants are poorly reported. Polystyrene nanoplastics (PSNPs) and arsenic (As) were used to assess their toxicity on Myriophyllum verticillatum L. via the orthogonal experiments. PSNPs significantly reduced the accumulation of As (17.24%-66.67%) in plant. Single As and high As-PSNPs treatments significantly inhibited plant growth, with a maximum reduction of 70.09% in the growth rate. The mineral nutrient content was significantly affected by PSNPs and As treatments. The antioxidant system was significantly inhibited, which was more pronounced in the roots. Similar findings were observed for soluble protein and soluble sugar. Some organic acids and amino acids showed down-regulation at high concentrations of As, leading to a decrease in the content of the mineral element and down-regulation of antioxidant enzyme synthesis. Furthermore, PSNPs could alleviate As toxicity under 0.1 mg/L As treatment but exacerbate As toxicity at 1 mg/L As dose. This study has important implications for the study of submerged plants exposed to co-contamination of microplastics and heavy metals, as well as the possible ecological risk assessment in freshwater.

Identifying global status and research hotspots of heavy metal remediation: A phase upgrade study

Impact of heavy metal (HM) pollution and its understanding on environment as well as human beings has grown a lot during the last few decades. The goal of this study is to create a scientometric study on heavy metal contamination, in the period 1989 to 2020, in order to provide futuristic goals for the new researchers on wastewater treatment. For this, a search was conducted in the Web of Science (WoS) and Scopus databases, related to heavy metal pollution. Totally, 37,154 records were collected during the study period from 1989 to 2020. The findings revealed that China, the United States, and India has most referenced papers across a wide range of trans disciplinary issues such as toxicity, technology, and pollution. As a result, this study concludes that more research on various treatment methods is required in order to obtain high-quality water for consumption and routine activities, with the incorporation of various treatment tasks poses various challenges for the upcoming future studies.

Comprehensive analysis of spatial distribution of microplastics in Rawal Lake, Pakistan using trawl net and sieve sampling methods

Occurrence of microplastics (MPs) in freshwater environments, particularly reservoir and lakes, is an emerging concern. There are limited studies in Pakistan on microplastic pollution in the lacustrine environments and those that exist do not provide sufficient information on the spatial distribution of MPs in offshore surface water. The aims of this study were to determine microplastic abundance in Rawal Lake, Pakistan and to ascertain if sampling methodology influences microplastic counts. Surface water samples were collected from 10 sites; 5 tributaries, 2 human settlement and 3 fishing and boating areas using two different sampling techniques: 100 μm mesh trawl and 20 L sample through a 45 μm mesh sieve. A significant difference was observed in the abundance of MPs across two methods with the sieve method yielding 2.8 ± 1.44 particles/L and trawl yielding 0.025 ± 0.024 particles/L. Tributaries and boating/fishing area had higher microplastic abundance than the residential area regardless of sampling method. Filaments were the dominant shape of MPs in both type of samples followed by fragments in trawl samples and films in sieved samples. Microbeads were only detected in trawl samples. MPs within size range 0.1-0.9 mm were mostly fragments (82%). MPs were diverse in colors with white/transparent and black MPs common. Polypropylene was the main type of microplastic in Rawal Lake (40-74%). Scanning Electron Microscopy (SEM) of MPs showed cracks, roughness and striations on the particles. Energy Dispersive Spectroscopy (EDS) detected heavy metals (Fe, Cu, Ni, Pb, Zn, Co and Cr) in MPs. Findings suggest that microplastic pollution in Rawal Lake may pose great risk to aquatic and human life through leaching of inherent/adsorbed heavy metals and therefore requires future investigation.

Comparison of epiphytic and intestinal bacterial communities in freshwater snails (Bellamya aeruginosa) living on submerged plants

The combination of submerged plants and snails can combat eutrophication of freshwater systems by suppressing algal growth and assimilating nutrients. By consuming epiphytes, snails can benefit the growth of submerged plants. However, the efficiency of this phytoremediation strategy may depend on the microbes associated with the plants and snails. In this study, we compared the epiphytic bacterial communities on submerged plants (Vallisneria natans and Cabomba caroliniana) and intestinal bacterial communities of a snail, Bellamya aeruginosa, found on these plants using 16S rRNA gene sequencing. Epiphytic bacterial communities were similar between the two plant species and snails shared a high proportion of snail intestinal bacterial OTUs (75%) and genera (85%) with plants they grazed on. However, significant variations of Bray-Curtis distances differentiated epiphytic and intestinal bacterial communities. In addition, between the top 50 genera shared by intestinal and epiphytic bacterial communities, more Spearman correlations were detected within bacterial communities associated with snails than between communities associated with plants (190 vs. 143), and the correlations in epiphytic bacterial networks were more concentrated on certain genera, indicating they possessed distinct bacterial networks. This suggests the bacterial communities associated with snails do not depend strongly on the plant they graze on, which may be important for better understanding the role of snails in aquatic eco-restoration.

Source apportionment and risk assessment of metal pollution in natural biofilms and surface water along the Lancang River, China

Herein, surface water and periphytic biofilm samples were collected from 16 sites along the Lancang River, China, to assess the spatial distribution, enrichment factor (EF), potential ecological risk index (RI), and associated source-oriented health risks of heavy metal elements (As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) in the samples. Results showed that the levels of heavy metals were significantly lower in the surface water samples than in the biofilm samples (one-way analysis of variance, p < 0.001). Moreover, 37.50 % of the biofilm samples were significantly polluted by these heavy metals with a mean EF of >5. As and V were the highest polluting metals, and the enrichment of Co and Ni were attributed to natural sources. RI assessment results showed a consistent ecological risk of As. Based on principal component analysis with multiple linear regression (PCA-MLR) and positive matrix factorization (PMF) models, the presence of heavy metal ions in the biofilm samples was largely attributed to industrial activities (PCA-MLR: 68.89 %; PMF: 76.39 %), followed by a mixed source of natural and agricultural activities (PCA-MLR: 18.12 %; PMF: 13.56 %), and traffic emissions (PCA-MLR: 12.99 %; PMF: 10.05 %). Both carcinogenic and noncarcinogenic risks for adults were negligible even though adults tended to be exposed to greater risk through ingestion. Source-specific risk evaluations indicated that industrial pollution was the most important source of health risks. Our findings highlight the potential threat of biofilms to the ecological and human health.

Heavy metal pollution in agricultural soils of a typical volcanic area: Risk assessment and source appointment

Heavy metals are naturally occurring elements with high natural background levels in the volcanic area. Therefore, it is necessary to conduct a risk assessment and identify potential sources of heavy metals. In this study, 4488 soil samples (0-20 cm) were collected in Chengmai County, a typical volcanic area in Hainan Province, and analyzed for eight heavy metals and major oxides. Pollution level, ecological risks, and health risks were evaluated by geo-accumulation index (I_geo), pollution index (PI), potential ecological risk index (RI), hazard index (HI), and carcinogenic risks (CR). The positive matrix factorization (PMF) model was further used to determine the priority source of heavy metals. The average values of heavy metal concentrations in soil were 7.06, 0.07, 156.88, 33.43, 0.05, 72.47, 19.48, and 67.51 mg kg^-1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively. Except for Pb, the average concentrations of all heavy metals exceeded background concentration in Hainan soils, indicating different degrees of heavy metal enrichment. The I_geo and PI showed that the main pollutant element in volcanic soils was Ni, followed by Cr and Cu. The RI shows that the percentage of soil samples with considerable or worse potential ecological risk was 44.4% of the total samples, with Hg, As, Cd, and Ni causing high ecological risks. The estimated average daily doses of heavy metals were below the tolerable limits and the HI values were below one for both adults and children, indicating that the residents had an acceptable potential non-carcinogenic risk. However, the potential carcinogenic risk of exposure to Cr, Ni, and As was unacceptable for residents, with high CR values exceeding 10^-4, especially for children. Based on the PMF, five major sources of heavy metals were found in the study area: Ni, Cu, and Zn mainly from parent materials, As and Pb from daily life and vehicle emissions, Cd from agricultural activities, Hg from industrial activities, and Cr from parent materials under different environmental conditions. Significant positive correlations between Al₂O₃, TFe₂O₃, Mn, soil organic carbon (SOC), and heavy metals reflect that aluminium-rich minerals, Fe-Mn oxides, and SOC are the most critical factors affecting heavy metal accumulation in volcanic agricultural soils.

A manganese-oxidizing bacterium-Enterobacter hormaechei strain DS02Eh01: Capabilities of Mn(II) immobilization, plant growth promotion and biofilm formation

While biogenic Mn oxides (BioMnO_x) generated by Mn(II)-oxidizing bacteria (MOB) have attracted increasing attention, a MOB strain isolated from Mn-polluted sediments was identified and assigned as Enterobacter hormaechei DS02Eh01. Its Mn(II) immobilization activity, plant growth-promoting traits, and biofilm formation capability were investigated. The results showed that strain DS02Eh01 was found to be able to tolerate Mn(II) up to 122 mM. The strain immobilized Mn(II) in aquatic media mainly through extracellular adsorption, bio-oxidation and pH-induced precipitation as well as manganese oxidation. DS02Eh01-derived BioMnO_x are negatively charged and have a larger specific surface area (86.70 m²/g) compared to the previously reported BioMnO_x. The strain can immobilize Mn(II) at extreme levels, for instance, when it was exposed to 20 mM Mn(II), about 59% of Mn(II) were found immobilized and 17% of Mn(II) were converted to MnO_x. The SEM and TEM observation revealed that the DS02Eh01-derived BioMnO_x were aggregates doped with granules and microbial pellets. The precipitated Mn(II) and the Mn(III)/Mn(IV) oxides co-existed in BioMnO_x, in which Mn(II) and Mn(IV) were found dominant with Mn(II) accounting for 49.6% and Mn(IV) accounting for 41.3%. DS02Eh01 possesses plant growth-promoting traits and biofilm formation capacity even under Mn(II) exposure. Mn(II) exposure at 5 mM was found to stimulate strain DS02Eh01 to form biofilms, from which, the extracted EPS was mainly composed of aromatic proteins. This study reveals that E. hormaechei strain DS02Eh01 possesses the potential in environmental ecoremediation via coupling processes of macrophytes extraction, biochemical immobilization and biosorption.

Effects of lead pollution on bacterial communities in biofilm attached to submerged plants

Submerged plants and biofilms have significant advantages in hydro-ecology rehabilitation, but their tolerance and physiological responses to heavy metal stress have thus far been under-investigated. This study investigated the influence of lead on physiological and biochemical responses, as well as variation in bacterial communities and functional characteristics of submerged plant biofilms. The results showed that chlorophyll a content of two submerged plants decreased with increased lead concentration. The concentration of malondialdehyde of both submerged plants was higher under high lead concentrations than under low lead concentrations, and the concentrations of malondialdehyde and hydrogen peroxide in Vallisneria natans were more stable. The antioxidant enzyme systems of the two plants played protective roles against lead stress. High lead concentration can inhibit the bacterial community and lead to decreased diversity. The most abundant bacterial phyla were Proteobacteria (40.9%), Cyanobacteria (21.5%), and Bacteroidetes (14.3%). Proteobacteria abundance decreased with increased lead concentration, while Cyanobacteria abundance increased. The lead concentration in plants (19.7%, P < 0.01) and the lead concentration in aquatic environment (17.7%, P < 0.01) were significantly correlated with variation in bacterial communities. High lead concentration inhibits the activity of these bacteria related to the conversion of nitrogen and sulfur.

ZAT10 plays dual roles in cadmium uptake and detoxification in Arabidopsis

Cadmium (Cd) is a harmful heavy metal that is risky for plant growth and human health. The zinc-finger transcription factor ZAT10 is highly conserved with ZAT6 and ZAT12, which are involved in Cd tolerance in plants. However, the definite function of ZAT10 in Cd tolerance remains uncertain. Here, we demonstrated that ZAT10 negatively regulated Cd uptake and enhanced Cd detoxification in Arabidopsis. The expression of ZAT10 in plants is induced by Cd treatment. The zat10 mutant plants exhibited a greater sensitivity to Cd stress and accumulated more Cd in both shoot and root. Further investigations revealed that ZAT10 repressed the transcriptional activity of IRT1, which encodes a key metal transporter involved in Cd uptake. Meanwhile, ZAT10 positively regulated four heavy metal detoxification-related genes: NAS1, NAS2, IRT2, and MTP3. We further found that ZAT10 interacts with FIT, but their regulatory relationship is still unclear. In addition, ZAT10 directly bound to its own promoter and repressed its transcription as a negative feedback regulation. Collectively, our findings provided new insights into the dual functions of ZAT10 on Cd uptake and detoxification in plants and pointed to ZAT10 as a potential gene resource for Cd tolerance improvement in plants.

Removal of perfluoroalkyl acids and dynamic succession of biofilm microbial communities in the decomposition process of emergent macrophytes in wetlands

Perfluoroalkyl acids (PFAAs) are emerging contaminants that pose significant environmental and health concerns. Water-sediment-macrophyte residue systems were established to clarify the removal efficiency of PFAAs, explore possible removal pathways, and profile the dynamic succession of biofilm microbial communities in the decomposition process. These systems were fortified with 12 PFAAs at three concentration levels. Iris pseudacorus and Alisma orientale were selected as the decomposing emergent macrophytes. The removal rates in the treatments with residues of I. pseudacorus (IP) and A. orientale (AO) were 34.4% to 88.9% and 36.5% to 89.9%, respectively, which were higher than those in the control groups (CG) (30.3% to 86.9%), suggesting that decomposition could alter the removal of PFAAs. Sediment made the greatest contributions (preloaded 14.5% to 77.8% of PFAAs in IP, 14.3% to 78.2% in AO, and 27.4% to 71.9% in CG). PFAAs could also be removed by macrophyte residue sorption (0.0190% to 13.0% in IP and 0.016% to 15.6% in AO) and bioaccumulation of residual biofilm (the contributions of biofilm microbes and their extracellular polymeric substances were 0.0110% to 3.93% and 0.918% to 34.4%, respectively, in IP and 0.0141% to 4.65% and 1.49% to 34.1%, respectively, in AO). Significant correlations were observed between sediment/residue adsorption and bioaccumulation of biofilm microbes, and were significantly correlated with perfluoroalkyl chain length (p < 0.05). The dynamic succession of residual biofilm microbial communities was investigated. The largest difference was found at the preliminary stage. The most similar communities were found in AO on day 70 (with specific genera Macellibacteroides and WCHB1-32) and in IP on day 35 (with specific genera Aeromonas and Flavobacterium). This study is useful to understand the removal of PFAAs during the decomposition process, providing further assistance in removing PFAAs during the life cycle of macrophytes in wetlands.

Streambed pollution: A comprehensive review of its sources, eco-hydro-geo-chemical impacts, assessment, and mitigation strategies

Streambeds are an integral part of the river ecosystem. They provide habitat to a vast array of aquatic and benthic organisms as well as facilitate the bio-degradation and transformation of organic matter and vital nutrients. Increasing anthropogenic influence introduces multiple stressors to the stream networks resulting in pollution of streambeds, which in turn, have detrimental effects on the overall stream ecosystem health. There is a huge gap in the current understanding of streambed pollution and its impacts, and the widely practiced streambed pollution mitigation strategies lack a holistic approach. In this comprehensive review, we first synthesize the state-of-the-art knowledge of conventional and emerging forms of contaminants, their overall impacts on stream ecosystem functions, and present future directions to comprehend the problem of streambed pollution. We highlight that fine sediments and plastics (found especially in urban streambeds) are among the major physical pollutants causing streambed pollution and the chemical pollutants generally comprise hydrophobic compounds including various legacy contaminants such as polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT), a wide range of pesticides and a variety of heavy metals. Moreover, in recent years, highly polar and hydrophilic emerging contaminants such as micro-plastics, pharmaceutical waste and personal care products have been identified in riverbeds and streambeds across the world. We stress that the impacts of streambed pollution have been largely studied with discipline-driven perspectives amongst which the ecological impacts have received a lot of attention in the past. To present a comprehensive outlook, this review also synthesizes and discusses most of the understudied hydrological, geomorphological and biochemical impacts of different forms of streambed pollution. Subsequently, we also present a global inventory by compiling information from the published literature to highlight the status of streambed pollution around the globe. In the end, we endorse the positive and negative aspects of the current impact assessment methodologies and also highlight various physical, chemical and biological remediation measures that could be undertaken to alleviate streambed pollution.

How to select substrate for alleviating clogging in the subsurface flow constructed wetland?

Constructed wetland (CW) is a cost-effective and environmentally friendly ecological technology for contaminated water remediation, especially in dispersed communities and rural areas. Plants grow, biofilms form, and pollutants attach to the substrate, which is the main supporting structure of a subsurface flow CW (SSFCW) system. After long-term operation, the accumulation of clogs from physical, chemical, and biological processes in SSFCW substrates can easily cause clogging, thus reducing treatment efficiency reduction and service life and causing no discharge of sewage by intermittent until last indicates in the CW surface. Subsequently, stench and mosquito breeding occur, thus influencing environmental sanitation. Substrate clogging is the most serious, challenging, and inevitable problem in the long-term operation of SSFCWs. The present study reviews the effects of substrates on clogging categorized into physical, chemical, and biological clogging and analyzes the substrates that can alleviate/aggravate clogging in CWs. The recommended substrates that can relieve clogging include plastic, rubber, soil mixture, walnut shell, biochar, organic waste, alum sludge, and lightweight aggregate, while shell, steel slag, blast furnace slag, zeolite, and soil may easily generate phosphorus-clogging substances. CW substrate clogging is a mixture of three clogs with synergistic effects, and the corresponding clogging mitigation substrates mentioned above can be used to alleviate the most severe among the three types of clogs to reduce the synergy, and thus to promote stable operation and technology level of CWs. This review aims to promote the scientific selection of substrates for the stable operation and technical level of CW through targeted recommendations for substrates that relieve clogging. Future studies should focus the effects of influent water quality and substrate type on clogging, and waste as substrate to alleviate clogging, while mitigating the negative environmental impact of waste treatment.

Ecotoxicological responses and removal of submerged macrophyte Hydrilla verticillate to multiple perfluoroalkyl acid (PFAA) pollutants in aquatic environments

The ubiquitous existence of perfluoroalkyl acids (PFAAs) in aquatic environments might pose toxic potential to ecosystems. To assess the ecotoxicological responses and removal of submerged macrophyte to multiple PFAA pollutants in aquatic environments, a typical submerged macrophyte, Hydrilla verticillate, was exposed to solutions with 12 typical PFAAs in the present study. The results showed that PFAAs at concentrations higher than 10 μg/L had significantly passive effects on biomass, relative growth rates, chlorophyll contents, and chlorophyll autofluorescence. PFAAs could induce the accumulation of hydrogen peroxide and lipid peroxidation in H. verticillate. Significant upregulation of CAT was observed in treatments with more than 10 μg/L PFAAs (p < 0.05). The results also showed that 13.53-20.01% and 19.73-37.72% of PFAAs could be removed in treatments without plants and with H. verticillate, respectively. The removal rates of PFAAs were significantly correlated with perfluoroalkyl chain length in treatments with H. verticillate. The removal of PFAAs was suggested to be related to the uptake of plant tissues and biosorption of microbiota. Furthermore, the dominant microbiota and biomarkers were identified in water and biofilm. Betaproteobacteriales was the most dominant microbiota at the order level. The presence of PFAAs could significantly increase the relative abundance of Micrococcales, Verrucomicrobiales, Rhizobiales, Sphingomonadales, Roseomonas, Cyanobium_PCC_6307, and Synechococcales. Our results provide scientific basis for evaluating the ecotoxicological responses and removal of submerged macrophytes in response to multiple PFAA pollutants at environmentally relevant levels, thereby providing insights into PFAA management and removal.

Metal analysis of submerged aquatic vegetation in the lower St. Johns River, Florida

The St. Johns River, Florida's longest river, is threatened by a variety of factors, including anthropogenic disturbances and global climate changes. Metal pollution in the Lower St. Johns River (LSJR) in Northeast Florida has been well documented. Submerged aquatic vegetation (SAV) are ecologically important plant species, known to accumulate metals and other pollutants from their surrounding environments, and have been declining in the LSJR in recent years. In this study, eight SAV taxa (Vallisneria americana, Ruppia maritima, Chara sp., Najas guadalupensis, Eleocharis sp., Hydrilla verticillata, Zannichellia palustris, and Sagittaria subulata) were collected along the LSJR from Central Florida northward to Jacksonville and the Atlantic Ocean. More than 200 SAV samples were identified, digested, and measured for a suite of metals. Mean (± standard deviation) metal concentrations in µg/g dry mass in all taxa sampled were 1.76 (± 2.75) cadmium, 35.8 (± 52.24) copper, 4.16 (± 5.74) lead, 119 (± 229) nickel, 0.98 (± 1.40) silver, and 203 (± 376) zinc. SAV metal concentrations varied across species and collection sites. In general, Z. palustris and Eleocharis sp. had the highest metal concentrations. Furthermore, a comparison of SAV metal concentrations to sediment quality guidelines for the LSJR indicated that toxicity may occur to biota exposed to these SAV. This study provides new data about SAV health in the LSJR and may help in the development of new management strategies.

Macroinvertebrate Assemblages along the Longitudinal Gradient of an Urban Palmiet River in Durban, South Africa

Urban rivers are regarded as unnatural because they drain catchments characterized by impervious surfaces. The present study explored macroinvertebrate communities in relation to water and habitat quality along the longitudinal gradient of an urban Palmiet River in Durban, South Africa. Sampling was conducted across six sites along the river. The water quality has shown a significant variation (ANOVA, p < 0.05) across six sites. Good-quality water was observed at Site 6, whereas Site 5 exhibiting hypertrophic condition. Sites 4 to 1 were all eutrophic; however, nutrient levels showed to decrease from Site 4 down to Site 2 and increased again at Site 1. A similar trend was observed for habitat quality, with Site 6 showing excellent and Site 5 exhibited poor habitat. Coinciding with water and habitat quality, macroinvertebrate diversity and abundance showed significant differences across six sites. Sensitive palaemonids, notonemourids, and amphipods were only observed in the headwaters and have contributed over 50% of the variation in abundance between Site 6 and other sites. The non-metric multidimensional scaling (NMDS) plot has also shown clear discrimination (MANOVA, p < 0.001) for the Average Score Per Taxon (ASPT) across the six sites. Macroinvertebrate communities have shown a clear association between water and habitat quality. These findings affirm the ecological importance of urban rivers as they provide refuge to aquatic biodiversity, with anthropogenic litter providing additional habitats for other taxa. Despite the current conditions supporting biodiversity and the functioning of the river, it is unclear if the system could endure further disturbance.

Synthetic Musk Fragrances in Water Systems and Their Impact on Microbial Communities

The presence of emerging contaminants in aquatic systems and their potential effects on ecosystems have sparked the interest of the scientific community with a consequent increase in their report. Moreover, the presence of emerging contaminants in the environment should be assessed through the “One-Health” approach since all the living organisms are exposed to those contaminants at some point and several works already reported their impact on ecological interactions. There are a wide variety of concerning emerging contaminants in water sources, such as pharmaceuticals, personal care products, house-care products, nanomaterials, fire-retardants, and all the vast number of different compounds of indispensable use in routine tasks. Synthetic musks are examples of fragrances used in the formulation of personal and/or house-care products, which may potentially cause significant ecotoxicological concerns. However, there is little-to-no information regarding the effect of synthetic musks on microbial communities. This study reviews the presence of musk fragrances in drinking water and their impact on aquatic microbial communities, with a focus on the role of biofilms in aquatic systems. Moreover, this review highlights the research needed for a better understating of the impact of non-pharmaceutical contaminants in microbial populations and public health.

Removal potential of multiple perfluoroalkyl acids (PFAAs) by submerged macrophytes in aquatic environments: Tolerance of Vallisneria natans and PFAA removal in submerged macrophyte-microbiota systems

Perfluoroalkyl acids (PFAAs) have emerged as a global concern in aquatic environment remediation due to their abundance, persistence, bioaccumulation, and toxicity. To comprehensively understand the removal potential of multiple PFAAs by submerged macrophytes in aquatic environments, systematic investigations into the tolerance of the typical submerged macrophyte Vallisneria natans to 12 typical PFAAs and the removal capacity to PFAAs in V. natans-microbiota systems were carried out. Results showed that although PFAAs could induce the accumulation of hydrogen peroxide and malondialdehyde, V. natans was overall resistant to multiple PFAAs with natural concentrations. Catalase is one of the main strategies of V. natans to alleviate PFAA stress. Microbiota can remove 18.10-30.84% of the PFAAs from the water column. 24.35-73.45% of PFAAs were removed from water in V. natans-microbiota systems. The uptake of plant tissues and the bioaccumulation of microbiota were proposed as the main removal processes. The removal rates were significantly correlated with the perfluorinated carbon atoms numbers (p < 0.05). PFAAs and V. natans increased the relative abundance of Betaproteobacteria, Nostocales, Microscillaceae, Sphingobacteriales, SBR1031, Chlamydiales, Phycisphaerae, Caldilineales, Rhodobacterales, and Verrucomicrobiales. The present study suggested that V. natans can be a potential species to remove multiple PFAAs in aquatic environments, and further providing insights into the PFAAs' remediation.

Caesium-133 Accumulation by Freshwater Macrophytes: Partitioning of Translocated Ions and Enzyme Activity in Plants and Microorganisms

The potential of aquatic plants to accumulate Cs may be of notable importance in the environmental monitoring of radioactive wastes. This study aimed to evaluate the accumulation of Cs-133 by freshwater macrophytes Bacopa amplexicaulis, Elodea densa, Ceratophyllum submersum, and Limnobium laevigantum after a 10-day incubation period with CsCl (1–1000 μM). The partitioning of Cs and other elements, including 21 metals, such as P, B, and As, was analyzed using inductively coupled plasma mass spectrometry combined with principal component analysis (PCA). The enzymatic activity of plant crude extracts and aquatic microorganisms was characterized. The transfer factor (TF) reached the highest values of 0.13 and 0.10 for C. submersum and L. laevigantum, respectively, at 1000 μM Cs. The TFs in the other sets were below 0.1. In the presence of Cs-133, there was a significant increase in dehydrogenase activity (p < 0.05) and a decrease in the activity of the Folin–Ciocalteu assay. A three-fold decrease in culturable microorganisms was found in plants with 1000 μM Cs. PCA analysis revealed the species-specific elemental distribution in plant biomass and the aquatic phase. A negative correlation between Na, Ca (2.0–2.5, PC1) and Mg, K, and P (−2, PC1) was found. Certain enzyme groups can serve as bioindicators of Cs pollution in aquatic ecosystems.

Oil Palm’s Empty Fruit Bunch as a Sorbent Material in Filter System for Oil-Spill Clean Up

Oil pollution such as diesel poses a significant threat to the environment. Due to this, there is increasing interest in using natural materials mainly from agricultural waste as organic oil spill sorbents. Oil palm’s empty fruit bunch (EFB), a cost-effective material, non-toxic, renewable resource, and abundantly available in Malaysia, contains cellulosic materials that have been proven to show a good result in pollution treatment. This study evaluated the optimum screening part of EFB that efficiently absorbs oil and the physicochemical characterisation of untreated and treated EFB fibre using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The treatment conditions were optimised using one-factor-at-a-time (OFAT), which identified optimal treatment conditions of 170 °C, 20 min, 0.1 g/cm³, and 10% diesel, resulting in 23 mL of oil absorbed. The predicted model was highly significant in statistical Response Surface Methodology (RSM) and confirmed that all the parameters (temperature, time, packing density, and diesel concentration) significantly influenced the oil absorbed. The predicted values in RSM were 175 °C, 22.5 min, 0.095 g/cm³, and 10%, which resulted in 24 mL of oil absorbed. Using the experimental values generated by RSM, 175 °C, 22.5 min, 0.095 g/cm³, and 10%, the highest oil absorption achieved was 24.33 mL. This study provides further evidence, as the data suggested that RSM provided a better approach to obtain a high efficiency of oil absorbed.

Simultaneous removal of Cd (II), Ni (II), and Pb (II) from water by a submerged macrophyte pondweed (Potamogeton malaianus)

The current work investigated the potential of submerged macrophyte pondweed (Potamogeton malaianus) in treating cadmium, nickel, and lead-contaminated water through phytoremediation. The adsorption for the three metal ions occurred rapidly within 2 h and attained dynamic equilibrium in no more than 72 h. The removal efficiencies of Cd (II), Ni (II), and Pb (II) were high, passing 94% in both single- and multi-metal systems. The kinetic adsorption curves of Cd (II), Ni (II), and Pb (II) were fitted well by both pseudo-first-order and pseudo-second-order kinetics (R²  = 0.9875-0.9995). The equilibrium adsorption capacities of Cd (II), Ni (II), and Pb (II) for P. malaianus were 6.29-6.97 mg kg^-1 . In plants, the higher concentration of each metal ions was accumulated in leaves (12.44-38.15 mg kg^-1 ) than in roots (10.32-26.10 mg kg^-1 ). The chlorophyll contents increased from 0.69 to 0.89-1.00 mg g^-1 under the treatment of Cd (II), Ni (II), and Pb (II), whereas the chlorophyll a/b ratio was kept constant. There was no significant difference between single- and multi-metal systems. FT-IR spectra showed that COH and C═N might be involved in the adsorption of Cd (II), Ni (II), and Pb (II). This study demonstrated that P. malaianus could be a suitable submerged macrophyte for the simultaneous removal of Cd (II), Ni (II), and Pb (II) from water.

Use of High-Performance Liquid Chromatography-Mass Spectrometry of Adipose Tissue for Detection of Bioaccumulation of Pyriproxyfen in Adults of Lithobates catesbeianus

The aims of the study were: (i) evaluate the efficacy of using amphibian adipose tissue as a valid biomarker of water contaminated by pyriproxyfen; and (ii) verify the use of Lithobates catesbeianus in laboratory experiments as a potential bioindicator for bioaccumulation of pesticide in adipose tissue from amphibians. Adult frogs were exposed to different dilutions (0.002 g/L and 0.02 g/L) of Sumilarv® (pyriproxyfen) over 50 days. The average results of the fortified sample were 108%, indicating that the test method was effective. Adult frogs exposed to the standard dose recommended by the World Health Organization (WHO) showed bioaccumulation of pyriproxyfen in adipose tissue significantly higher than control animals. Lithobates catesbeianus proved to be an effective bioindicator and the adipose tissue was an efficient biomarker to bioaccumulation of pyriproxyfen. We conclude that high-performance liquid chromatography-mass spectrometry was effective measuring pyriproxyfen bioaccumulation in adult amphibians.

Unfolding the interaction between microplastics and (trace) elements in water: A critical review

Plastic and microplastic pollution is an environmental and societal concern. The interaction of plastic with organic chemicals in the environment has attracted scientific interest. New evidences have highlighted an unexpectedly high affinity of environmental plastics also for metal ions. The degree and typology of plastic ageing (including from mechanical, UV and biological degradations) appear as a pivotal factor determining such an interaction. These earlier evidences recently opened a new research avenue in the plastic pollution area. This review is the first to organize and critically discuss knowledge developed so far. Results from field and laboratory studies of metal accumulation on plastic are presented and the environmental factors most likely to control such an interaction are discussed. On the light of this knowledge, a generalist conceptual model useful for building hypotheses on the mechanisms at stake and directing future studies was elaborated and presented here. Furthermore, all available data on the thermodynamics of the plastic-metal interaction obtained from laboratory experiments are inventoried and discussed here, highlighting methodological and technical challenges that can potentially affect cross-comparability of data and their relevance for environmental settings. Finally, insights and recommendations on experimental approaches and analytical techniques that can help overtaking current limitations and knowledge gaps are proposed.

Submerged macrophytes recruit unique microbial communities and drive functional zonation in an aquatic system

Aquatic and wetland systems are widely used for landscapes and water regeneration. Microbiomes and submerged macrophytes (hydrophytes) play essential roles in conversions of organic and inorganic compounds in those ecosystems. The systems were extensively investigated for microbial diversities and compositions. However, little is known about how hydrophytes recruited diverse microbiota and affected functional zonation in aquatic systems. To address this issue, epiphytic leaf and root, sediment, and surrounding water samples were collected from the dragon-shape aquatic system in Beijing Olympic Park. Metagenomic DNAs were extracted and subjected to sequencing. Results showed that epiphytic leaf and root microbiomes and metabolic marker genes were remarkably different from that of surrounding environment. Twenty indicator bacterial genera for epiphytic microbiomes were identified and 50 metabolic marker genes were applied to evaluate the function of epiphytic leaf and root, water, and sediment microbiomes. Co-occurrence analysis revealed highly modularized pattern of metabolic marker genes and indicator bacterial genera related to metabolic functions. These results suggested that hydrophytes shaped microbiomes and drove functional zonation in aquatic systems. KEY POINTS: • Microbiomes of hydrophytes and their surrounding environments were investigated. • Twenty indicator bacterial genera highly specific to epiphytic biofilms were identified. • Epiphytes recruited unique microbiomes and drove functional zonation in aquatic systems.

Nickel bioaccumulation by a marine bacterium Brevibacterium sp. (X6) isolated from Shenzhen Bay, China

Nickel bioaccumulation capacity of a marine Brevibacterium sp., designated as X6, was evaluated to explore its potential application in the bioremediation of Ni²⁺ pollutants in marine environments. The minimum Ni²⁺ inhibitory concentration and maximum Ni²⁺ bioaccumulation of X6 were 1000 mg/L and 100.95 mg/g, respectively, higher than most reported strains. Among the co-existing metal ions in seawater, K⁺ caused a slight adverse impact on Ni²⁺ uptake, followed by Na⁺ and Ca²⁺, whereas Mg²⁺ drastically inhibited Ni²⁺ bioaccumulation. Other heavy metals such as Co²⁺, Zn²⁺ and Cd²⁺ moderately affected Ni²⁺ binding, but the adverse effect of Cu²⁺ was severe. The investigation of the mechanism of Ni²⁺ bioaccumulation revealed that 66.34% of the accumulated Ni²⁺ was bound to the cell surface. Carboxylic, hydroxyl, amino and thiol groups participated in Ni²⁺ binding, while carboxylic group contributed the most, while thiol group may be more involved in Ni²⁺ binding at low Ni²⁺ concentrations.

Role of intertidal microbial communities in carbon dioxide sequestration and pollutant removal: A review

Intertidal microbial communities occur as biofilms or microphytobenthos (MPB) which are sediment-attached assemblages of bacteria, protozoa, fungi, algae, diatoms embedded in extracellular polymeric substances. Despite their global occurrence, they have not been reviewed in light of their structural and functional characteristics. This paper reviews the importance of such microbial communities and their importance in carbon dioxide sequestration as well as pollutant bioremediation. Global annual benthic microalgal productivity was 500 million tons of carbon, 50% of which contributed towards the autochthonous carbon fixation in the estuaries. Primary production by MPB was 27-234 gCm^-2y^-1 in the estuaries of Asia, Europe and the United States. Mechanisms of heavy metal removal remain to be tested in intertidal communities. Cyanobacteria facilitate hydrocarbon degradation in intertidal biofilms and microbial mats by supporting the associated sulfate-reducing bacteria and aerobic heterotrophs. Physiological cooperation between the microorganisms in intertidal communities imparts enhanced ability to utilize polycyclic aromatic hydrocarbon pollutants by these microorganisms than mono-species communities. Future research may be focused on biochemical characteristics of intertidal mats and biofilms, pollutant-microbial interactions and ecosystem influences.

Mechanisms underlying mercury detoxification in soil-plant systems after selenium application: a review

Feasible countermeasures to mitigate mercury (Hg) accumulation and its deleterious effects on crops are urgently needed worldwide. Selenium (Se) fertilizer application is a cost-effective strategy to reduce Hg concentrations, promote agro-environmental sustainability and food safety, and decrease the public health risk posed by Hg-contaminated soils and its accumulation in food crops. This holistic review focuses on the processes and detoxification mechanisms of Hg in whole soil-plant systems after Se application. The reduction of Hg bioavailability in soil, the formation of inert HgSe or/and HgSe-containing proteinaceous complexes in the rhizosphere and/or roots, and the reduction of plant root uptake and translocation of Hg in plant after Se application are systemically discussed. In addition, the positive responses in plant physiological and biochemical processes to Se application under Hg stress are presented to show the possible mechanisms for protecting the plant. However, application of high levels Se showed synergistic toxic effect with Hg and inhibited plant growth. The effectiveness of Se application methods, rates, and species on Hg detoxification is compared. This review provides a good approach for plant production in Hg-contaminated areas to meet food security demands and reduce the public health risk.

ЗАСТОСУВАННЯ МЕТОДУ ІНВЕРСІЙНОЇ ХРОНОПОТЕНЦІОМЕТРІЇ ДЛЯ КОНТРОЛЮ ВМІСТУ ТОКСИЧНИХ ЕЛЕМЕНТІВ У РАФІНАЦІЙНОМУ ВИРОБНИЦТВІ

Вступ. Україна є одним з провідних світових експортерів соняшникової олії. Важливим показником безпечності є вміст у ній токсичних елементів, який не повинен перевищувати гранично допустимі концентрації. Токсичні речовини, потрапляючи в організм людини, знижують функції окремих систем і органів та призводять до імунодефіцитного стану організму. До токсичних елементів, за якими контролюються харчові продукти належать купрум (Cu), цинк (Zn), ферум (Fe), кадмій (Cd), плюмбум (Pb), арсен (As) та меркурій (Hg).Проблематика. Не дивлячись на значний прогрес фізико-хімічних методів аналізу, визначення токсичних елементів у сировині, напівфабрикатах та харчових продуктах є складним та проблемним, а питання розробки методів їх ідентифікації є актуальним.Мета. Порівняння методів інверсійної хронопотенціометрії (ІХП) та атомної абсорбції при визначенні вмісту токсичних елементів в соняшниковій олії на різних стадіях технологічного процесу її виробництва.Матеріали і методи. Соняшникову олію, одержану пресуванням та екстрагуванням, та суміш пресової з екстракційною різного ступеня очищення (гідратовану, нейтралізовану, вінтеризовану та рафіновану дезодоровану) досліджено методами ІХП та атомної абсорбції. При визначенні концентрації токсичних елементів методом ІХП встановлено тривалість інверсії анодного розчинення йонів металів, які попередньо були накопичені у процесі електролізуна поверхні індикаторного електроду.Результати. Аналіз зразків олії свідчить про те, що всі вони містять токсичні елементи, концентрація яких зменшується на кожній стадії виробництва олії, проте не перевищує допустимих рівнів, регламентованих нормативними документами.Висновки. Результати дослідження створюють передумови для широкого впровадження методу ІХП на рафінаційному виробництві, оскільки цей метод дозволяє визначати вміст токсичних елементів в рослинних оліях з високою збіжністю результатів відносно традиційно застосовуваного методу атомної абсорбції.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N₂ (BC-N) and CO₂ (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g^-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Profiling metal contamination from ultramafic sediments to biota along the Albanian shoreline of Lake Ohrid (Albania/Macedonia)

Ultramafic sediments exhibit high levels of geogenically-derived and potentially toxic metals, with Ni, Cr and Co often exceeding benchmark values. As yet, a holistic understanding of the bioavailability, mobility, potential ecotoxicity and trophic transfer of trace elements in both benthic and pelagic food chains in aquatic ultramafic environments (UME) is lacking. We investigated potential environmental health issues due to metal contamination by jointly implementing chemical, ecological and toxicological tools, along the Albanian shoreline of Lake Ohrid. It is an aquatic system of worldwide importance, representative of temperate UME with a legacy of Ni and Cr contamination from mining activities. Levels of Ni, Cr, Cd, Cu, Co, Fe, Mn and Zn were determined in waters, sediments and native biota. The potential environmental mobility of sediment-bound elements was further assessed using CaCl₂, EDTA and acetic acid extractions. Whole-sediment ecotoxicity tests were also carried out using ostracods and chironomids, according to standardized procedures. Despite Ni and Cr concentrations above the sediment quality guidelines for probable effect levels, we did not observe ecotoxic effects in laboratory tests. However, these elements were bioavailable to native organisms under field conditions, especially to benthic primary producers in direct contact with sediments (up to 139 mg Cr kg^-1 and 785 mg Ni kg^-1). Although biomagnification was not observed, further investigations of metal translocation, metabolism and elemental trophic transfer along benthic food webs appears to be a general research priority in the management of temperate UME. The present study shows that proper management of temperate UME requires not only the integration of data from different lines of evidence, but also laboratory vs. field approaches to understand the subtler, long-term effects of increased elemental body burdens in native organisms.

Ecofriendly remediation technologies for wastewater contaminated with heavy metals with special focus on using water hyacinth and black tea wastes: a review

Treatment of water contaminated with heavy metals is challenging. Heavy metals are non-degradable, persistent in the environment, have a high dispersion capacity by water, can bioaccumulate, and represent risks to human and environmental health. Conventional treatment methods have disadvantages; however, adsorption in biomass is a highly promising method with high efficiency and low cost that avoids many of the disadvantages of conventional methods. Black tea (BT) wastes and water hyacinth (WH) have attracted attention for their ability to remove heavy metals from wastewater. Utilizing these approaches can remove contaminants and effectively manage problematic invasive species and wastes. The conventional uses of BT and WH were efficient for removing heavy metals from wastewater. Due to the unique and distinct properties and advantages of biochar and nano-forms of biosorbents, the use of BT and WH in these forms is promising to achieve sustainable heavy metals removal from wastewater. However, more study is needed to confirm preliminary results.

Removal of perfluoroalkyl acids (PFAAs) in constructed wetlands: Considerable contributions of submerged macrophytes and the microbial community

The broad application of perfluoroalkyl acids (PFAAs) has attracted global concern regarding their adverse environmental effects. The possible removal processes of PFAAs in constructed wetlands were excavated and quantified using two typical submerged macrophytes (rooted Potamogeton wrightii and rootless Ceratophyllum demersum). Our results showed that 33.59-88.99% of PFAAs could be removed via not only sediment sorption or phytoextraction but also by the bioaccumulation of microbiota. The sediment acts as a vital sink for PFAAs, preloading 23.51-50.09% and 16.65-52.18% of PFAAs in treatments with P. wrightii (Pw1) and C. demersum (Cd1), respectively. C. demersum showed a better capacity to accumulate PFAAs (0.91-32.03%) than P. wrightii (<10%). Considerable PFAAs were observed to be distributed in microbes, underlining the non-negligible role of microbiota in bioaccumulating PFAAs. The contributions of planktonic microbes, biofilm microbes, and extracellular polymeric substances in biofilms were 0.39-20.96%, 0.03-7.95%, and 0.39-14.15% in Pw1 and 0.23-15.68%, 0.01-15.68%, and 0.53-26.77% in Cd1, respectively. The adsorption/uptake was significantly correlated with the perfluoroalkyl chain length (p<0.05), except for the uptake of biofilms in C. demersum. Furthermore, PFAAs and submerged macrophytes could decrease the richness of microbiota but increase the relative abundance of some strains in Betaproteobacteriales, Sphingomonadales, and Cytophagales. Our results were helpful for understanding the removal processes of PFAAs in constructed wetlands and their linkages with PFAA properties, thus further providing insight into the management and removal of emerging organic contaminants.

Constructed wetland, an eco-technology for wastewater treatment: A review on types of wastewater treated and components of the technology (macrophyte, biolfilm and substrate)

Constructed wetland (CW) represents an efficient eco-technological conglomerate interweaving water security, energy possibility and environmental protection. In the context of wastewater treatment technologies requiring substantial efficiency at reduced cost, chemical input and low environmental impact, applications of CW is being demonstrated at laboratory and field level with reasonably high contaminant removal efficiency and ecological benefits. However, along with the scope of applications, role of individual wetland component has to be re-emphasized through related research interventions. Hence, this review distinctively explores the concerns for extracting maximum benefit of macrophyte (focusing on interface of pollutant removal, root radial oxygen loss, root iron plaque, endophyte-macrophyte assisted treatment in CW, and prospects of energy harvesting from macrophyte) and role of biofilm (effect on treatment efficiency, composition and factors affecting) in a CW. Another focus of the review is on recent advances and developments in alternative low-cost substrate materials (including conventional type, industrial by-products, organic waste, mineral based and hybrid type) and their effect on target pollutants. The remainder of this review is organized to discuss the concerns of CW with respect to wastewater type (municipal, industrial, agricultural and farm wastewater). Attempt is made to analyze the practical relevance and significance of these aspects incorporating all recent developments in the areas to help making informed decisions about future directions for research and development related to CW.

Validation of Hydrocharis morsus-ranae as a possible bioindicator of trace element pollution in freshwaters using Ceratophyllum demersum as a reference species

The assessment of trace metal pollution in aquatic environments remains a challenge. Chemical methods are insufficient and bioindicators seem to be the most promising alternative. Finding an adequate species is important to ensure accurate data. The combined use of several bioindicators may help to overcome the limitations of species' spatial distribution and specific reactions. The aims of the present study were to compare the contents and bioaccumulation capability of 11 trace elements in Ceratophyllum demersum and different organs of Hydrocharis morsus-ranae and to validate H. morsus-ranae as a bioindicator of pollution in aquatic reservoirs using C. demersum, an established bioindicator, as a reference species. The application of several statistical techniques allowed us to identify similarities in accumulation patterns and concentration gradients between the two species. The results showed that concentrations of Cd, Co, Cr, Cu, Mn, Ni, Pb, Rb, Zn, V in C. demersum and roots of H. morsus-ranae were similar and mostly higher than in the leaves and stems of H. morsus-ranae. The contents of Cd, Co, Cr, Li, Mn, Ni, Rb, V, Zn were positively correlated. The inner transport of metals in H. morsus-ranae was limited (TF < 1). Both species are accumulators (BF > 10³) of Ni and Zn, and H. morsus-ranae also of Cu and Pb. Frog-bit roots were chosen to be most promising in bioindication. Major axis regression analysis showed that the uptake of Cd, Cr, Co, Li and Pb was similar in the two species. Neural networks demonstrated substantial uniformity in responses of C. demersum and roots of H. morsus-ranae to the type of anthropogenic activity and land use and similar spatial distributions of Cd, Cr, Co, Li and Pb. When Nemerow Pollution Index was applied, both species showed congruent gradients of contamination. Thus, H. morsus-ranae was validated as a reliable bioindicator of trace metal pollution in freshwater.

A review on phytoremediation of mercury contaminated soils

Mercury (Hg) and its compounds are one of the most dangerous environmental pollutants and Hg pollution exists in soils in different degrees over the world. Phytoremediation of Hg-contaminated soils has attracted increasing attention for the advantages of low investment, in-situ remediation, potential economic benefits and so on. Searching for the hyperaccumulator of Hg and its application in practice become a research hotspot. In this context, we review the current literatures that introduce various experimental plant species for accumulating Hg and aided techniques improving the phytoremediation of Hg-contaminated soils. Experimental plant species for accumulating Hg and accumulation or translocation factor of Hg are listed in detail. The translocation factor (TF) is greater than 1.0 for some plant species, however, the bioaccumulation factor (BAF) is greater than 1.0 for Axonopus compressus only. Plant species, soil properties, weather condition, and the bioavailability and heterogeneity of Hg in soils are the main factors affecting the phytoremediation of Hg-contaminated soils. Chemical accelerator kinds and promoting effect of chemical accelerators for accumulating and transferring Hg by various plant species are also discussed. Potassium iodide, compost, ammonium sulphate, ammonium thiosulfate, sodium sulfite, sodium thiosulfate, hydrochloric acid and sulfur fertilizer may be selected to promote the absorption of Hg by plants. The review introduces transgenic gene kinds and promoting effect of transgenic plants for accumulating and transferring Hg in detail. Some transgenic plants can accumulate more Hg than non-transgenic plants. The composition of rhizosphere microorganisms of remediation plants and the effect of rhizosphere microorganisms on the phytoremediation of Hg-contaminated soils are also introduced. Some rhizosphere microorganisms can increase the mobility of Hg in soils and are beneficial for the phytoremediation.

Comprehensive review of the basic chemical behaviours, sources, processes, and endpoints of trace element contamination in paddy soil-rice systems in rice-growing countries

Rice is the leading staple food for more than half of the world's population, and approximately 160 million hectares of agricultural area worldwide are under rice cultivation. Therefore, it is essential to fulfil the global demand for rice while maintaining food safety. Rice acts as a sink for potentially toxic metals such as arsenic (As), selenium (Se), cadmium (Cd), lead (Pb), zinc (Zn), manganese (Mn), nickel (Ni), and chromium (Cr) in paddy soil-rice systems due to the natural and anthropogenic sources of these metals that have developed in the last few decades. This review summarizes the sources and basic chemical behaviours of these trace elements in the soil system and their contamination status, uptake, translocation, and accumulation mechanisms in paddy soil-rice systems in major rice-growing countries. Several human health threats are significantly associated with these toxic and potentially toxic metals not only due to their presence in the environment (i.e., the soil, water, and air) but also due to the uptake and translocation of these metals via different transporters. Elevated concentrations of these metals are toxic to plants, animals, and even humans that consume them regularly, and the uniform deposition of metals causes a severe risk of bioaccumulation. Furthermore, the contamination of rice in the global rice trade makes this a critical problem of worldwide concern. Therefore, the global consumption of contaminated rice causes severe human health effects that require rapid action. Finally, this review also summarizes the available management/remediation measures and future research directions for addressing this critical issue.

Potential of invasive watermilfoil (Myriophyllum spp.) to remediate eutrophic waterbodies with organic and inorganic pollutants

Watermilfoil (Myriophyllum) is one of the world's most troublesome invasive aquatic weeds. Although current management practices may inhibit its expansion, it also impacts not only the quality of water but habitat deterioration. Therefore, the need for developing highly efficient and low-cost biotechnologies with resource recovery into the agriculture field as a complementary management strategy cannot be overstated. Here, we reviewe the scientific/grey literature to offer readers a precise and panoramic view of the invasive watermilfoil ecology, regional problems, impacts, ecosystem services, and management. In this regard, an in-depth review aimed to assess the potential for reducing non-point source inorganic and organic pollutants using invasive watermilfoil, with the sustainable approaches, while offering other services and mitigating ecological trade-offs is presented. Global distributions, growth, and current progress on the management and utilization of invasive watermilfoil biomass are summarized to develop the aim, which is to convey challenges during the implementation of large-scale weed use. In short, pollutant assimilation in plant and bacterial communities linked to this weed considerably contribute to the reduction and degradation of pollutants from both natural and artificial systems. Although several considerations in recycling and reusing biomass need to be considered, the potential reuse of the harvested material for livestock feed, compost and direct use in farming systems offer an additional strategy to achieve sustainable ecosystem restoration. Further research and development may focus on a more detailed economic modeling approach that integrates the costs (worker's wage, harvesting, transportation, and energy consumption), legal and regulatory barriers, health risks and ecosystem service benefits (biodiversity improvement, and pollutant removal) to holistically evaluate the economic, environmental, and societal value of reusing and recycling this waste material.

The use of Callitriche cophocarpa Sendtn. for the reclamation of Cr-contaminated freshwater habitat: benefits and limitations

This work is the first attempt to evaluate suitability of Callitriche cophocarpa Sendtn. (water-starwort) to remove Cr under real-world conditions. Our earlier laboratory-scale studies demonstrated outstanding hyperaccumulation properties of this aquatic higher plant (macrophyte) toward chromium in solution. We introduced C. cophocarpa plants into the watershed with sediments heavily polluted (on average 1400 mg/kg d.w. of Cr) by a tannery. The plants grew vigorously and exhibited no physiological or anatomical disorders. Based on chemical fractionations of bottom sediments, we found low Cr bioavailability. The element was strongly associated with the sediments and could be classified into the following fractions (%): oxidizable III (68.2) > residual IV (28.8) > reducible II (1.6) > exchangeable I (1.4). Despite this, Cr content in plant organs at the contaminated sites was 33 up to 83 times greater than in the control leaf/stem and roots, respectively. Altering redox potential during, i.e., sediment deposition on land may change chemical forms of bound metals in a solid phase, and thus further increase Cr phytoextraction by plants. With this in mind, we concluded that the species, being an outstanding Cr accumulator under laboratory conditions, can be useful in the reclamation of Cr-polluted sediments under controlled, oxidizing conditions.